1. Field of the Invention
This invention relates to the technique of automatically controlling the movement of a lens bv electrical signals for application to the field of photographic instruments such as cameras having drive devices for movable lenses and to the field of business machines such as copiers having drive devices for movable lenses, and more particularly to lens drive devices using piezoelectric material.
2. Description of the Prior Art
The technique of automatically controlling adjustment of a movable lens to a desired position, for example, to an in-focus position, has found use in many automatic focus adjusting devices.
As a typical example of an automatic focus adjusting apparatus mention may be made of the lens moving apparatus disclosed in Japanese Laid-Open Patent Application No. Sho 54-80741. In this lens moving apparatus, the movable lens is contained in the holder sleeve urged by a spring member toward the position for an object at infinity or at the minimum distance, and, as it moves from the opposite position thereto, it is arrested by a focusing control signal from the in-focus detector.
The operating mechanism for the movable lens in the above-described automatic focus adjusting apparatus and in many other prior art devices necessitates utilization of a great number of constitutent parts, such as the drive spring member and the arresting member in the form of a plunger, and involves a complicated assembling process. On the assembly line, it is also necessary to introduce the step of adjusting each unit. This impedes to a much desired reduction in the production cost of the article.
Further prior art devices involving lens moving apparatus are disclosed in Japanese Laid-Open Patent Applications Nos. Sho 57-92321 and Sho 57-92322 and U.S. Pat. No. 4,291,958.
The above-cited three prior art examples concern lens moving apparatus using a piezoelectric element called "piezoelectrically operated lens motor" and sold under the tradename of "Bimorph" from Vernitron Co. Ltd. This lens motor according to the above-described Japanese Laid-Open Patent Applications is constructed in the form of a 30 mm long, 0.5 mm thick and 5.0 mm wide plate (rod) of piezoelectrically operated bender element with its one end fixedly supported and its opposite end fixedly carrying a lens holder frame. When a voltage is applied, the bender element is distorted to effect axial movement of the lens holder.